In a digital transmission of a mobile communication system and the like, due to a multipath fading caused by reflection by a building and the like, the level of a receiving signal changes by large amounts temporally so that code errors such as burst errors occur. Thus, various error correcting codes are used. In the error correcting codes, an interleaving technique is used for improving correcting ability for the burst error. The proprieties of the interleaving technique determines the ability of the error correcting code for the burst error.
As is known to a person skilled in the art, the object of the interleaving method is to randomize a sequence of input bit series and a sequence of output bit sequence. FIG. 1 shows an example of the interleaving method according to a conventional technique. In this figure, an example is shown in which interleaving process is performed to data 101 of one frame which is configured by 1152 bits. An array 110 has a buffer of N×M (N rows and M columns). The interleaving process is realized such that, for example, 16 bits are written to this buffer in the row direction like a row vector 115 which is indicated by a diagonally shaded area A and 72 bits are read out in the column direction like a column vector 120 which is indicated by a diagonally shaded area B.
By the way, it is becoming required that various apparatuses in the mobile communication multiplex a plurality of channels for data transmission. FIG. 2 shows an example of a data multiplexer according to a conventional technique. The data multiplexer 30 includes channel coding parts 32, 34, transmission line interleavers 36, 38, frame segmenting parts 40, 42, a sub-block/multiplexing part 44 and a physical channel mapping part 46. The frame is assumed to be a fixed time length which is the same as the minimum interleaving span.
In the figure, the channel coding part 32, the transmission line interleaver 36 and the frame segmenting part 40 perform an interleaving process of a logical channel A and the channel coding part 34, the transmission line interleaver 38 and the frame segmenting part 42 perform an interleaving process of a logical channel B. The interleaving process is performed, for example, by the above-mentioned method.
The logical channel A has a coding block size LA and an interleaving span IA. The logical channel B has a coding block size LB and an interleaving span IB. The interleaving span IA is not necessarily the same as the interleaving span IB. In each channel, each of the frame segmenting part 40, 42 performs segmentation for multiplexing after performing error correction and interleaving, then multiplexing is performed segment by segment. According to the configuration, the difference between interleaving spans of channels is absorbed. In addition, the sub-block/multiplexing part divides frame data of each channel into sub-blocks having proper size beforehand and multiplexes each channel data alternately by the sub-block such that bits of the two logical channels are distributed uniformly over frames as possible.
By the way, in the field of the mobile communication, since the mobile station moves at high velocity, it is necessary to keep stable operation even under an environment of a high fading pitch. Therefore, it is performed to send pilot signals which indicate reference phase of modulation in a predetermined cycle. An interval between a pilot signal and next pilot signal is called a slot in which data signals are placed. Then, a receiving side which receives signals configured by the slot obtains the reference phase in a slot interval by using interpolation based on a pilot signal in the head part of the slot and a pilot signal in the end part of the slot. Then, the receiving side performs synchronous detection based on the reference phase which is interpolated. This method of obtaining the reference phase adaptively is often called synchronous detection using interpolation pilot signal. There are various methods similar to this method, in which, it is generally performed that interpolation coefficients are decided according to time from each pilot signal.
It is performed to transmit burst data for performing variable rate data transmission. In terms of this case, a technique has been developed in which data signals in one slot are placed to be adjacent to the pilot signal (TECHNICAL REPORT OF IEICE, RCS95-166).
With respect to this point, a concrete description will be given with reference to FIG. 3. FIG. 3 is a figure which shows relationships between the pilot signal and the data signals according to a conventional technique. In this example, the interval of one slot is 1 msec. In addition, when the transmission rate of the data signals is 32 kbps, 32 bit data signals are placed between the pilot signals PS in which continuous transmission is performed. On the other hand, when the data transmission rate is lower than 32 kbps, burst transmission is performed. For example, when the transmission rate is 16 kbps, as shown in the figure, 16 bits of data signals are placed adjacent to the pilot signal PS in the head part of the slot.
However, in the data multiplexer 30 according to the conventional technique, each of the transmission line interleaver 36, 38 needs to perform different bit interleaving for input data of different block sizes and different interleaving spans. Therefore, there is a problem in that the process is not performed effectively.
In the data transmit/receive method using the above-mentioned interpolation pilot signal, when S/N of the transmission line is low so that transmission quality is bad, high level noise is superimposed in received pilot signals. Thus, large error is included in a phase measuring result by using the pilot signal PS. As mentioned above, the reference phase in a slot interval is adaptively estimated in which interpolation coefficients are decided according to times from the pilot signals PS of the head part and the end part. Therefore, near the pilot signal PS, noise is not uniformed so that estimation error becomes large. Thus, there is a problem in that, when data signals are placed adjacent to the pilot signal PS of the head part, a large influence is exerted on the phase so that the transmission quality is deteriorated.
On the other hand, when noise is enough small or the fading pitch is high, influence of phase change due to fading is larger than that due to noise. In this case, transmission quality can be improved by placing data signals near the pilot signal PS.
Solutions for the above-mentioned problems of the data transmit/receive method are proposed in Japanese patent application No. 8-111644. However, an interleaving method applicable for flattening data quality in a flame when data bits are interleaved is not disclosed.